Synthesis of ZSM-12

ABSTRACT

This invention provides a process for the synthesis of ZSM-12 using the N,N-dimethylhexamethyleneimine cation as a directing agent. The process enables ZSM-12 to be produced at silica/alumina molar ratios below 50 with little or no co-production of impurity phases. Small crystal forms of ZSM-12 can also be produced using the process of the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to application Serial No.60/266,527, filed Feb. 5, 2001, which is hereby incorporated byreference.

FIELD OF THE INVENTION

[0002] This invention relates to a process for the synthesis of theporous crystalline material ZSM-12, to ZSM-12 produced by said process,and to use of the resultant ZSM-12 as a catalyst for organic compound,e.g., hydrocarbon compound, conversion.

[0003] More particularly, this invention relates to a process forsynthesizing aluminosilicate ZSM-12 having a low silica to alumina molarratio and substantially free of impurity phases.

Discussion of the Prior Art

[0004] ZSM-12 and its conventional preparation in the presence of atetramethylammonium or tetraethylammonium directing agent are taught byU.S. Pat. No. 3,832,449, the entire disclosure of which is incorporatedherein by reference. ZSM-12 has a distinctive X-ray diffraction patternwhich distinguishes it from other known crystalline materials.

[0005] U.S. Pat. No. 4,391,785 discloses a method for the synthesis ofZSM-12 from a reaction mixture comprising, as a directing agent, acompound selected from the group consisting of a dimethyl pyridiniumhalide and a dimethyl pyrrolidinium halide.

[0006] U.S. Pat. Nos. 4,452,769 and 4,537,758 disclose methods forsynthesizing ZSM-12 from a reaction mixture containingmethyltriethylammonium ions as the directing agent.

[0007] Other organic directing agents that have been used to synthesizeZSM-12 include bis (dimethylpiperidinium) trimethylene ions (see U.S.Pat. No. 4,539,193), benzyltriethylammonium ions (see U.S. Pat. No.4,552,738), dimethyldiethylammonium ions (see U.S. Pat. No. 4, 552,739),benzyltrimethylammonium ions (see U.S. Pat. No. 4,585,637), bis(N-methylpyridyl) ethylinium ions (see U.S. Pat. No. 4,5852,746) and bis(methylpyrrolidinium)-dicuat-n, where n=4, 5 or 6 (see U.S. Pat. No.5,192,521).

[0008] Hexamethyleneimine has been used as a directing agent tosynthesize a variety of different crystalline structures, includingMCM-22 (U.S Pat. No. 4,954,325), MCM-35 (U.S. Pat. No. 4,981,663) andZSM-12 (U.S. Pat. No. 5,021,141). In particular, the examples of U.S.Pat. No.5,021,141 disclose the use of hexamethyleneimine to synthesizeZSM-12 with silica/alumina mole ratios varying between 62 and 852.ZSM-12 synthesized using hexamethyleneimine as the directing agent tendsto crystallize as large hexagonal platelets having edge dimensions ofabout 2000nni.

[0009] Existing methods for the synthesis of ZSM-12 suffer from theproblem that they tend to produce impurity phases, such as ZSM-5,especially when at product silica/alumina molar ratios less than 100.According to the present invention, it has now been found that a noveldirecting agent, the N,N-dimethylhexamethyleneimine cation, can be usedto synthesize ZSM-12 at silica/alumina molar ratios below 50 with littleor no coproduction of impurity phases. In addition, ZSM-12 synthesizedusing the N,N-dimethylhexamethyleneimine cation as the directing agenttends to crystallize as small crystals with dimensions of about 50 nm.

[0010] It is to be appreciated that, although ZSM-12 is normallysynthesized as an aluminosilicate, the framework aluminum can bepartially or completely replaced by other trivalent elements, such asboron, iron and/or gallium, and the framework silicon can be partiallyor completely replaced by other tetravalent elements such as germanium.

SUMMARY OF THE INVENTION

[0011] According to the invention, there is provided a process forsynthesizing the porous, crystalline material ZSM-12 which comprises thesteps of:

[0012] (i) preparing a mixture capable of forming said material, saidmixture comprising sources of alkali or alkaline earth metal (M), anoxide of trivalent element (X), an oxide of tetravalent element (Y),hydroxyl (OH) ions, water and N,N-dimethylhexamethylenceimine ions (R),wherein said mixture has a composition, in terms of mole ratios, withinthe following ranges:

YO₂/X₂O₃=at least 30

H₂O/YO₂ =30-70

OH/YO₂=0.15-0.45

M/YO₂=0.15-0.45

R/YO₂=0.20-0.55,

[0013] (ii) maintaining said mixture under sufficient conditions untilcrystals of said material are formed; and

[0014] (iii) recovering said crystalline material from step (ii).

[0015] Preferably, said reaction mixture has a composition in terms ofmole ratios within the following ranges:

YO₂/X₂O₃=40-200

H₂O/YO₂=35-45

OH/YO₂=0.30-0.40

M/YO₂=0.20-0.40

R/YO₂=0.30-0.45.

[0016] Preferably, M is sodium.

[0017] Preferably, said mixture also contains a source oftetramethylammonium ions.

DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 shows the X-ray diffraction pattern of the as-synthesizedproduct of Example 1.

[0019]FIG. 2 shows the X-ray diffraction pattern of the as-synthesizedproduct TABLE 1 D-spacing (Å) Relative Intensity [100 × I/Io] 11.9 ±0.2  m 10.1 ± 0.2  m 4.76 ± 0.1  w 4.29 ± 0.08 vs 3.98 ± 0.08 m 3.87 ±0.07 vs 3.49 ± 0.07 w 3.38 ± 0.07 m 3.20 ± 0.06 w 3.05 ± 0.05 w 2.54 ±0.03 w

[0020] of Example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The ZSM-12 produced by the process of the invention has an X-raydiffraction pattern, characterized by the X-ray diffraction lines inTable 1 below:

[0022] These X-ray diffraction data were collected with a Scintagdiffractometer using copper K-alpha radiation. The diffraction data wererecorded by step-scanning at 0.02 degrees of two-theta, where theta isthe Bragg angle, and a counting time of 1 second for each step. Theinterplanar spacings, d's, were calculated in Angstrom units (A), andthe relative intensities of the lines, I/Io, where Io is one-hundredthof the intensity of the strongest line, above background, were derivedwith the use of a profile fitting routine (or second derivativealgorithm). The intensities are uncorrected for Lorentz and polarizationeffects. The relative intensities are given in terms of the symbolsvs=very strong (75-100), s=strong (50-74), m=medium (25-49) and w=weak(0-24). It should be understood that diffraction data listed for thissample as single lines may consist of multiple overlapping lines whichunder certain conditions, such as differences in crystallite sizes orvery high experimental resolution or crystallographic change, may appearas resolved or partially resolved lines. Typically, crystallographicchanges can include minor changes in unit cell parameters and/or achange in crystal symmetry, without a change in topology of thestructure. These minor effects, including changes in relativeintensities, can also occur as a result of differences in cationcontent, framework composition, nature and degree of pore filling, andthermal and/or hydrothermal history.

[0023] The crystalline material ZSM-12 prepared hereby has a compositioninvolving the molar relationship:

[0024] X₂O₃:(n)YO2

[0025] wherein X is a trivalent element, such as aluminum, boron, iron,indium and/or gallium, preferably aluminum; Y is a tetravalent element,such as silicon, tin and/or germanium, preferably silicon; and n is atleast 30 and more usually from about 40 to about 200. In theas-synthesized form, the crystalline material prepared hereby has aformula, on an anhydrous basis and in terms of moles of oxides per nmoles of YO₂, as follows:

[0026] (0.05 to 4.0)M₂O:(0 to 1.0) TMA₂O:(0.2 to 25)R₂O:X₂O₃:(n)YO2

[0027] wherein M is an alkaline or alkaline earth metal, R is theN,N-dimethylhexamethyleneimine cation and TMA is the tetramethylammoniumcation. The M, TMA and R components are associated with the material asa result of their presence during crystallization, and are easilyremoved by post-crystallization methods hereinafter more particularlydescribed.

[0028] The particular effectiveness of the presently required organicdirecting agent, the N,N-dimethylhexamethyleneimine cation, as comparedwith other directing agents, for the present synthesis is in its abilityto produce ZSM-12 with a silica/alumina molar ratio below 100, and morepreferably below 50 with little or no coproduction of impurity phases.In view of its increased aluminum content, it is believed that theZSM-12 produced by the process of the invention will have an enhancedactivity when used as an acid catalyst in reactions such as hydrocarbonconversion.

[0029] The ZSM-12 produced by the present process also tends to havesmaller crystal size than that produced by conventional methods andhence should exhibit reduced mass transfer limitations.

[0030] The process of the invention involves initially producing asynthesis mixture containing sources of alkali or alkaline earth metal(M) cations, normally sodium, an oxide of a trivalent element (X),normally alumina, an oxide of a tetravalent element (Y), normallysilica, N,N-dimethylhexamethyleneimine ions (R), normally present as theiodide salt, hydroxyl ions and water. The synthesis mixture has acomposition, expressed in terms of mole ratios of oxides, as follows:Component Useful Preferred YO₂/X₂0₃ At least 30  40-200 H₂O/YO₂ 30-7035-45 OH⁻/YO₂ 0.20-0.45 0.30-0.40 R/YO₂ 0.20-0.55 0.30-0.45 M/YO₂0.15-0.45 0.20-0.40

[0031] The N,N-dimethylhexamethyleneimine iodide directing agent isconveniently prepared from commercially available hexamethyleneimine(HMI) by reacting 1 mol of HMI with 3 moles of methyl iodide in 300 mlof chloroform. First a solution of HMI in chloroform is prepared andmethyl iodide is added gradually over 30 minutes. The mixture isrefluxed overnight. The product is precipitated with 500 ml of THFfiltered and dried at room temperature. The dried product isre-dissolved in 80 ml of chloroform and precipitated with 100 ml THF,filtered and dried at room temperature.

[0032] The ZSM-12 synthesis mixture may also contain tetramethylammoniumions, normally the hydroxide (TMAOH), such that the TMA/YO₂ molar ratiois from about 0 to about 0.3.

[0033] The synthesis method of the invention functions with or withoutadded nucleating seeds. In a preferred embodiment, the reaction mixturecontains 0.05-5 wt % nucleating seeds of ZSM-12.

[0034] Crystallization is carried out under either stirred or staticconditions at a temperature of 130 to 200° C., preferably 150 to 175°C., for 48 hours to 14 days and the resultant crystals are separatedfrom the mother liquor and recovered.

[0035] When the only organic medium present in the synthesis mixture isN,N-dimethylhexamethyleneimine, the ZSM-12 produced by the process ofthe invention tends to be in the form of small crystals with a diameterof about 50 nm aggregated into irregular clusters with cross sectionaldimensions of about 200

[0036] ZSM-12 synthesized by the process of the invention contains theorganic material(s) used as the directing agent and, prior to use as acatalyst or adsorbent, the as-synthesized material is normally treatedto remove part or all of the organic constituent. This is convenientlyeffected by heating the as-synthesized material at a temperature of fromabout 250° C. to about 550° C. for from 1 hour to about 48 hours.

[0037] To the extent desired, the original sodium and/or potassiumcations of the as-synthesized material can be replaced in accordancewith techniques well known in the art, at least in part, by ion exchangewith other cations. Preferred replacing cations include metal ions,hydrogen ions, hydrogen precursor, e.g., ammonium ions and mixturesthereof. Particularly preferred cations are those which tailor thecatalytic activity for certain hydrocarbon conversion reactions. Theseinclude hydrogen, rare earth metals and metals of Groups IIA, IIIA, IVA,VA, IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIII of the Periodic Table ofthe Elements.

[0038] The crystalline material of this invention, when employed eitheras an adsorbent or as a catalyst in an organic compound conversionprocess should be dehydrated, at least partially. This can be done byheating to a temperature in the range of 200° C. to about 370° C. in anatmosphere such as air or nitrogen, and at atmospheric, subatmosphericor superatmospheric pressures for between 30 minutes and 48 hours.Dehydration can also be performed at room temperature merely by placingthe ZSM-12 in a vacuum, but a longer time is required to obtain asufficient amount of dehydration.

[0039] Synthetic ZSM-12 crystals prepared in accordance herewith can beused either in the as-synthesized form, the hydrogen form or anotherunivalent or multivalent cationic form. It can also be used in intimatecombination with a hydrogenating component such as tungsten, vanadium,molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noblemetal such as platinum or palladium where ahydrogenation-dehydrogenation function is to be performed. Suchcomponents can be exchanged into the composition, impregnated therein orphysically intimately admixed therewith. Such components can beimpregnated in or on to the ZSM-12 such as, for example, by, in the caseof platinum, treating the material with a platinum metal-containing ion.Suitable platinum compounds for this purpose include chloroplatinicacid, platinous chloride and various compounds containing the platinumamine complex. Combinations of metals and methods for their introductioncan also be used.

[0040] When used as a catalyst, it may be desirable to incorporate theZSM-12 prepared hereby with another material resistant to thetemperatures and other conditions employed in certain organic conversionprocesses. Such matrix materials include active and inactive materialsand synthetic or naturally occurring zeolites as well as inorganicmaterials such as clays, silica and/or metal oxides, e.g. alumina,titania and/or zirconia. The latter may be either naturally occurring orin the form of gelatinous precipitates, sols or gels including mixturesof silica and metal oxides. Use of a material in conjunction with theZSM-12, i.e. combined therewith, which is active, may enhance theconversion and/or selectivity of the catalyst in certain organicconversion processes. Inactive materials suitably serve as diluents tocontrol the amount of conversion in a given process so that products canbe obtained economically and orderly without employing other means forcontrolling the rate or reaction. Frequently, crystalline catalyticmaterials have been incorporated into naturally occurring clays, e.g.bentonite and kaolin. These materials, i.e. clays, oxides, etc.,function, in part, as binders for the catalyst. It is desirable toprovide a catalyst having good crush strength because in a petroleumrefinery the catalyst is often subjected to rough handling, which tendsto break the catalyst down into powder-like materials which causeproblems in processing.

[0041] Naturally occurring clays which can be composited with the herebysynthesized crystalline material include the montmorillonite and kaolinfamilies which include the subbentonites, and the kaolins commonly knownas Dixie, McNamee, Georgia and Florida clays, or others in which themain mineral constituent is halloysite, kaolinite, dickite, nacrite oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment or chemicalmodification.

[0042] In addition to the foregoing materials, the present crystals canbe composited with a porous matrix material such as silica-alumina,silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,silica-titania, as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia. The matrix can be in the form of a cogel.A mixture of these components could also be used.

[0043] The relative proportions of finely divided crystalline materialand matrix vary widely with the crystalline material content rangingfrom about 1 to about 90 percent by weight, and more usually in therange of about 2 to about 50 percent by weight of the composite.

[0044] Aluminosilicate ZSM-12 produced by the process of the inventionis useful as a catalyst in organic compound, and in particularhydrocarbon, conversion reactions where high activity is important. Inparticular, when combined with a hydrogenation component, such asplatinum, palladium or rhenium, the ZSM-12 is useful in transalkylationof toluene with heavier, C₉+, alkylaromatics and the dealkylation ofethyl- and propyl-aromatics, such as ethylbenzene.

[0045] In order to more fully illustrate the nature of the invention andthe manner of practicing same, the following examples are presented.

Example 1

[0046] A gel having the following molar composition was prepared fromdistilled water, silica (HiSil 233), a 50wt % aqueous sodium hydroxidesolution, sodium aluminate and N,N-dimethylhexamethyleneimine iodide(R):

[0047] SiO_(2:)0.025Al₂O_(3:)0.2Na₂O:0.3R:40H₂O.

[0048] Zeolite crystallization was conducted by heating the gel underautogenous pressure at 150° C. for 168 hours without stirring. Theresultant zeolite product was filtered, washed and dried. X-ray analysiswas conducted on the dried, as-synthesized product with a Scintagdiffractometer using copper K-alpha radiation and with the diffractiondata being recorded by step-scanning at 0.05 degrees of two-theta and acounting time of 1 second for each step. The X-ray pattern indicated theproduct to be ZSM-12 without visible impurity phases (FIG. 1), althoughthe X-ray lines showed evidence of broadening suggesting a smallcrystallite size. This was confirmed by scanning electron microscopywhich showed the ZSM-12 product to be in the form of irregularaggregates, around 200 nm in diameter, of small crystallites having anaspect ratio of nearly I and a diameter of 50 mm or less.

[0049] Elemental analysis of the crystalline product of Example 1indicated a silica/alumina molar ratio of 39.

Example 2

[0050] A gel having the following molar composition was prepared fromdistilled water, silica (HiSil 233), a 50 wt % aqueous sodium hydroxidesolution, sodium aluminate, tetramethylammonium hydroxide (TMAOH) andN,N-dimethylhexamethyleneimine iodide (R):

[0051] SiO_(2:)0.025Al₂O_(3:)0.125Na₂O:0.1TMAOH:0.3R:40H₂O.

[0052] Zeolite crystallization was conducted as in Example 1 and theresultant zeolite product was filtered, washed and dried. X-ray analysiswas conducted on the dried, as-synthesized product with a Scintagdiffractometer using copper K-alpha radiation and with the diffractiondata being recorded by step-scanning at 0.02 degrees of two-theta and acounting time of 10 seconds for each step. The X-ray pattern showed theproduct to be ZSM-12 without visible impurity phases (FIG. 2).

What is claimed is:
 1. A process for synthesizing the crystallinematerial ZSM-12 which comprises the steps of: (i) preparing a mixturecapable of forming said material, said mixture comprising sources ofalkali or alkaline earth metal (M), an oxide of trivalent element (X),an oxide of tetravalent element (Y), hydroxyl (OH-) ions, water andN,N-dimethylhexamethyleneimine cations (R), wherein said mixture has acomposition, in terms of mole ratios, within the following ranges:YO₂/X₂O₃=at least 30 H₂O/YO₂=30-70 OH/YO₂=0.15-0.45 M/YO₂=0.15-0.45R/YO₂=0.20-0.55, (ii) maintaining said mixture under sufficientconditions until crystals of said material are formed; and (iii)recovering said crystalline material from step (ii).
 2. The process ofclaim 1, wherein said reaction mixture has a composition in terms ofmole ratios within the following ranges: YO₂/X₂O₃=40-200 H₂O/YO₂=35-45OH/YO₂=0.30-0.40 M/YO₂=0.20-0.40 R/YO₂=0.30-0.45.
 3. The process ofclaim 1, wherein M is sodium.
 4. The process of claim 1, wherein saidmixture also contains a source of tetramethylammonium cations.
 5. Theprocess of claim 1, wherein said mixture further comprises seed crystalsin sufficient amount to enhance synthesis of said crystalline material.6. The process of claim 5, wherein said seed crystals have the structureof ZSM-12.
 7. The process of claim 1, wherein X is selected from thegroup consisting of aluminum, boron, iron, gallium, indium and mixturesthereof, and said Y is selected from the group consisting of silicon,germanium, tin and mixtures thereof.
 8. The process of claim 1, whereinX comprises aluminum and Y comprises silicon.
 9. ZSM-12 synthesized bythe process of claim
 1. 10. A method for converting a feedstockcomprising an organic compound to a conversion product which comprisescontacting said feedstock at organic compound conversion conditions witha catalyst comprising an active form of the ZSM-12 synthesized by theprocess of claim
 1. 11. The method of claim 10 wherein the organiccompound is toluene and the conversion is transalkylation with a C₉+alkylaromatic compound.
 12. The method of claim 10 wherein the organiccompound is ethylbenzene or propylbenzene and the conversion isdealkylation.